Aluminium formate and process of making the same



Patented Oct. 29, 1935 UNITED STATES ALUBIINIUM FORMATE AND PROCESS OF MAKING THE SAME Greiz-Dolau, Germany Application April 12, 1933, Serial No Drawing.

No. 665,840. In Germany April 18, 1932 4 Claims.

The object of this invention is to make a solid aluminium formate recrystallizable from water solutions and the'product thereof.

The aluminium salts of the lower fatty acids, for example aluminium formate and aluminium acetate, are mainly employed for impregnation in the textile industry and for pharmaceutical purposes; They are principally on the market in the form of fairly dilute aqueous solutions, such as, for example, aluminium acetate in the form of a 7.5 to 8% solution. Repeated attempts have already been made to manufacture concentrated solutions or even solid products of the aluminium salts of lower fatty acids. So far, however, these attempts have failed to produce satisfactory results, firstly because in the con-' centration of the solutions turbidity and deposits frequently occur, and secondly because the evaporation and drying causes decomposition and escape of free fatty acids. Furthermore, the solid end products obtained by the processes known heretofore were generally either not at all soluble, or only partly soluble, in water.

It has already been proposed to manufacture water-soluble crystalline aluminium formate by evaporating an aluminium formate solution in the presence of an excess of formic acid until a film appears and leaving the solution to crys tallize at a temperature of 25-30 C. The crys talline aluminium formate so obtained cannot be recrystallized from an aqueous solution, and obviously, therefore, it is not stable in aqueous solutions. In this known manner of manufacture a considerable expenditure of heat is neces sary and loss of formic acid occurs. This process has not obtained any practical importance.

It has furthermore been proposed to manufacture water-soluble basic aluminium acetate and aluminium formate by drying the aqueous solutions of these aluminium salts in a finely atomized form. Even in the case of this process, it is not possible to work without considerable expen diture of heat for the evaporation of the large quantities of water, and furthermore a complicated and expensive apparatus is required for this purpose. In this process also no crystals are obtained but only more or less finely-divided dry residues, which still contain all the impurities of the original solutions.

It has now been found that aluminium salts of the lower fatty acids, more particularly aluminium acetate and aluminium formate, may be manufactured without the expenditure of heat and without loss of fatty acids, by mixing aqueous solutions of the aluminium salts of lower fatty acids with the corresponding free fatty acids in excess and leaving the salt solution, thus acidified, to itself, without evaporating down, at the ordinary temperature for some time, if neces sary with agitation. In this way, crystalline aluminium salts may be obtained from a solution of aluminium formate of a specific gravity of- 1.045 and from a solution of aluminium acetate of a specific gravity of 1.015. According to the observations which have been made up to the present, these concentrations ought not to be considered as the minimum concentrations nec-' essary for the success of the process. In prac-' tice, starting solutions of higher concentration are preferably employed, for example, a solution of aluminium acetate of a specific, gravity of 1.075 to 1.100. Complete separation of the salts present in the starting solutions does not take place, but the mother liquors may be employed again. The-excess of free acids may be selected as desired within wide limits.

Ithasfurtherbeen found that, by using sufficiently strong aqueous aluminium formate solu tions, water-soluble crystalline aluminium formate may be obtained even without the addition of free formic acid. Apparently, aluminium formate forms slightly supersaturated solutions, which separate crystalline aluminium formate only when they are left to themselves for some time at the ordinary temperature, if desired with agitation.

Aluminium formate solutions with a specific gravity of 1.100 only exhibit slightcrystal formation after several weeks when no free formic acid is added. The specific gravity of 1.100 may therefore be regarded as the minimum concentration for the manufacture of aluminium formate without the addition of free formic acid. Aluminium formate solutions of higher concentration yield large quantities of crystalline aluminium formate even in a short time.

The adjustment of the aluminium salt solutions to the desired specific gravity may be effected by the reaction of suitable quantities of aluminium sulphate, calcium carbonate, and the lower fatty acids in question.

The separation of the crystals from the aluminium salt solution may be assisted by adding slight quantities of the desired crystalline aluminium salt as inoculating substance, if desired after the addition of the free fatty acid.

The crystal formation is likewise promoted by constant or occasional agitation.

The crystalline aluminium salts obtained may be readily separated from the mother liquor by filtration. The aluminium formate may be washed without difiiculty with water, dried and recrystallized from water.

The mother liquors remaining after the separation of the crystals may be employed again for new mixtures for the manufacture of crystalline aluminium salt, if desired. with the free fatty acid contained in the said mother liquors.

Examples agitated for three days at the ordinary temperature. The crystalline aluminium formate deposited is separated by filtration, washed with water and dried in the air at 50 0. Yield: 3 kilograms.

3. 10 litres of an aluminium formate solution adjusted to a specific gravity of 1.152, the analysis of which gives 84.4 grams A1203 and 201 grams H.COOI-I per litre, is left to itself at the ordinary temperature with occasional agitation. After 120 hours, 50 grams of crystalline aluminimum formate will have seperated out, the analysis of which gives 12.54 per cent. Al, 62.42 per cent. I-I.COOI-I and the remainder 25.04 per cent. water, and which thus corresponds to the formula Al(HCOO) 3.3H2O.

4. 10 litres of an aluminium formate solution adjusted to a specific gravity of 1.220, the analysis of which gives 125.5 grams A1203, and 336 grams H.COOI-I per litre, is mixed at the ordinary temperature with 50 grams of crystalline aluminium formate as inoculating substance and is then left to itself with occasional agitation. After 65 hours, '2580 grams of crystalline aluminium formate of the same composition as in Example 3 will have separated out. 5

The present invention represents a considerable technical advance, because by means thereof it is possible to obtain aluminium salts of the lower fatty acids, such as for example aluminium formate and aluminium acetate, in a crystalline water-soluble form on a technically satisfactory scale from aqueous solutions.

We claim:

1. The method of preparing water-soluble crystalline aluminium formate which comprises 1 adding, at ordinary temperatures, formic acid to an aqueous aluminium formate solution of at least 1.045 specific gravity, and immediately thereupon leaving the acidified solution to itself at ordinary room temperatures for some time with agitation, and separating the crystals from the mother liquor.

2. The method of preparing water-soluble crystalline aluminium formate which comprises preparing, at ordinary temperatures, an aluminium formate solution of at least 1.100 specific gravity and leaving the solution to itself to crystallize without application of heat thereto.

3. The method of preparing water-soluble crystalline aluminium formate which comprises preparing, at ordinary temperatures, an aluminium formate solution of at least 1.100 specific gravity, adding a small quantity of crystalline aluminium formate, agitating for some time at ordinary temperatures and separating the crys-. tals from the solution, the entire process being carried out without application of heat.

4. Solid aluminium formate of the formula Al(HCOO)3.3H2O, exhibiting the property of recrystallizing from aqueous solutions.

OSKAR JOCHEM. THEODOR HENNIG. 

